1. Field Of The Invention
The present invention relates to methods for treating kaolin clays for the purpose of obtaining an improved dried paint film gloss when incorporated in organic solvent-based paint formulations, and water-based paint formulations and for the purpose of imparting significantly improved gloss ink holdout in paper coating films. Numerous attempts have been made in the prior art in order to provide a filler clay material which when used as a high gloss filler for alkyd paints, latex paints, and paper coatings, provides improvement in sheet optical quality and improvement in gloss ink holdout properties, and requires less total coating solids.
2. Prior Art
It is well known and conventional to use inexpensive particulate materials such as refined clays and calcium carbonate to provide increased opacity in paints and paper. Various methods of improving the opacity, brightness, and gloss, among other properties of pigments and fillers, are known to those skilled in the art. In particular, titanium dioxide additions to coating systems containing pigments and fillers of low refractive indices substantially improved the opacities of those coating systems.
Clay is advantageously used as the entire mineral extender, in paints and coatings. Other typical extender materials include calcium carbonate, diatomaceous earth, and asbestine.
The mineral extenders of moderate cost that are generally commercially employed are the purified high kaolinite clays.
Methods of producing kaolin pigments are shown in U.S. Pat. No. 3,615,806. The kaolin pigment is obtained by delaminating kaolin clay particles of not less than five microns e.s.d. and then removing particles of less than two microns e.s.d., so that the remainder is the product used. The product is then dried and pulverized to produce the final product which is useful in exterior paints. The product will disperse in both aqueous and non-aqueous systems without any special chemical surface treatment. The resultant product has superior enamel holdout and hiding in the applied paint film, which thus has a very uniform low sheen. In a test paint formulation the product of the above-mentioned U.S. patent includes titanium dioxide, kaolin clay, Igepal 610, ethylene glycol, NH.sub.4 OH as well as other ingredients. Although Igepal 610 is used in the final test paint formulation, there is no disclosure or suggestion of surface treating the clay particles with any surfactant prior to using the particles in the formulation of paints. In any event, this patent teaches away from the present invention by suggesting that surface treatment of clay with surfactants renders it useless in aqueous systems. Furthermore, the paints produced by this prior patent have a low sheen, not the improved gloss provided by this invention.
In U.S. Pat. No. 3,453,131, clay particles having a negative electrical charge are adhered to functional colloidal pigment particles by aliphatic organic acid which acts as a coupling agent. The composite particles are formed in aqueous suspension which can be used, or dried composite particles may be recovered. This is useful in cosmetic preparations, paint formulations, or wherever clay is used as a carrier for another particle used for coloration. There is no disclosure in this patent of the treatment of clay with a nonionic surfactant.